1. Field of The Invention
The present invention relates to an apparatus for controlling AC elevators, and more specifically to a control apparatus for AC elevators, in which an induction motor for driving an elevator cage is controlled by using a frequency converter.
2. Description of The Related Art
Recently, as disclosed in, for example, Japanese Utility Model Laid-open Publication No. 56-132274, an elevator control system has been developed, according to which an induction motor for driving an elevator cage is controlled by using a frequency converter (called an inverter device, hereinafter). Such an inverter device usually has a converter unit capable of converting AC electric power to DC electric power, a smoothing capacitor connected across output terminals of the converter unit for smoothing the output voltage of the converter unit and an inverter unit connected to the converter unit and inverting the converted DC electric power into AC electric power. The AC electric power of the constant frequency, which is supplied to the inverter device from a commercial electric source, is converted to the AC electric power of the variable frequencies, which is fed to the induction motor.
With this, the induction motor can be very effectively controlled from the start of the elevator to the stop thereof, by varying the output voltage and frequency of the inverter device. Consequently, the consumption of the electric power is much improved, and in addition the high accuracy in the control can be attained.
As is well known, voltage and current controlled by the inverter device include a large quantity of and various kinds of harmonics, which cause noise. Especially, in the case of elevator facilities, the inverter device and various kinds of control equipment are usually accommodated in a unitary control cubicle, and therefore there is the possibility that noise generated in the inverter device easily enters the control equipment and is emitted everywhere inside a building through a tail code which connects the elevator cage and the control equipment and communicates signals and electric power therebetween, or through wirings which are provided within the building for signal communication between the control equipment and devices such as hall call button switches and indicators equipped in elevator halls of floors.
The emitted noise causes interference in other electric appliances, such as audio appliances, computors and the like, existing within the building. This problem is more serious, because the elevator usually works near office rooms or living rooms.